The present invention relates generally to chemical spraying of agricultural fields from an aircraft and, more particularly, to a control system and method for applying chemicals to an agricultural field wherein the chemicals are automatically released over the field as the aircraft travels along an appropriate flight pattern. Radio frequency signals from global positioning satellites are used to determine the instantaneous position of the aircraft relative to the flight pattern and the field.
Chemical spraying of field crops and orchards has long been widespread in the agricultural industry. During aerial spraying of chemicals on an agricultural field, the aircraft makes numerous sequential, adjacent passes, spraying a swath across the field during each pass. The aircraft pilot must carefully guide the aircraft to ensure that each of the successive traverses over the field is laterally spaced from the adjacent traverse by the proper distance in order to avoid either gaps or overlaps in spraying coverage. As will be appreciated, overlaps in spraying coverage result in spraying more chemicals on the field than desired. This is costly and may cause crop damage. Gaps between swaths, on the other hand, leave untreated areas in which crop growth may be poor.
Several methods for controlling swath width and placement have been devised in the past. For instance, commonly assigned U.S. Pat. No. 4,225,226 issued to Davidson et al discloses a laser guidance system for crop spraying aircraft. The crop spraying aircraft carries a rotating laser transmitter and receiver to transmit a laser beam onto a plurality of ground reflectors located at known positions relative to each other and to detect the subsequently reflected laser beams. The angular position of the aircraft is then determined by a microprocessor based on the reflected laser beams. Any deviation from a predetermined spraying path results in a microprocessor-generated error signal.
Other methods for controlling swath width and Location include using ground personnel holding flags at either end of the field to provide visual guidance to the aircraft pilot and dropping materials on the field from a dispenser mounted on the aircraft to provide a visual ground reference for the aircraft pilot on the next traverse. Numerous problems exist with the above described methods. The high chemical concentrations used by modern crop spraying aircraft, which allow such aircraft to cover larger areas with a given payload, have increased the health hazards associated with using ground personnel in close proximity to the chemical spraying. Further, overlapping of these higher concentration chemicals can damage or destroy crops to a greater degree.
Additional problems with previous systems involve the requirement of adjacent traverses and the manual operation of the chemical spraying device. To make sequential, adjacent traverses of a field, the pilot is required to execute a key-hole turn at the end of each pass. A key-hole turn consists, for example, of a 45 degree left turn, a 270 degree right turn and another 45 degree left turn in succession. The short radius turns and sharp turning angles required in previous methods significantly increase the possibility of aircraft aerodynamic stall.
Prior chemical spraying systems also require that the aircraft pilot identify the proper time to release the chemicals at the beginning of the swath and the proper time to shut off the spraying device at the end of the swath. Typically, these judgments are made based on visual perception of the aircraft pilot. Failure to turn the spraying device on or off correctly results in unsprayed crops or overspraying into neighboring land.
Accordingly, the need exists in the art for an improved control system and method for applying chemicals to an agricultural field by aircraft which dynamically detects position changes of the aircraft, automatically activates and deactivates the chemical spraying at the beginning and ending boundaries of the field, permits increases in the radius turn and turning angle of the flight paths, provides more accurate swath path control, allows alteration of the directional orientation of the swaths for optimal spraying coverage, and provides increased swath control to ensure uniform chemical coverage throughout the field.